a. Field of the Invention
The present invention relates to an improved apparatus and method for the regeneration of spent wet active carbon, and more particularly it relates to the treatment of the spent carbon that is exhausted from water pollution control devices.
B. Description of the Prior Art
The regeneration of spent carbon seems to be generally performed through three steps of drying, calcination and reactivation by supplying the spent carbon-to-be-treated, batchwise or continuously, into a chamber made of materials having a good thermal conductivity and a heat resistance and installed inside a heating furnace and introducing regeneration steam into said chamber while heating the chamber externally. In the case of the conventional regeneration apparatuses as prevalently employed, granting that it varies with the construction of apparatus, the degree of wetness of the spent carbon, the applied amount of regeneration steam, etc., about 50% of the quantity of heat supplied to the regeneration chamber is generally consumed in evaporating the moisture from the spent carbon, so that, at present, these apparatuses are being operated under the condition that the degree of contribution of the supplied heat to the calcination and reactivation actions, which are most important in the regeneration operation, is restricted that much.
The present inventors have previously proposed, in the Japanese patent Application No. 7484/1973, a regeneration apparatus for spent carbon, wherein a vertical outer cylinder having a feed inlet for the spent carbon-to-be-treated provided on the upper end and an outlet for discharging the resulting product in a fixed quantity provided on the lower end thereof is installed centrally in a vertical heating furnace having at least one burner, and at least one duct with a damper, an inner cylinder sealed at the lower end thereof having a regeneration gas supply tube and a duct with a damper is inserted centrally in said outer cylinder, a multiplicity of inclined annular plates with a slope steeper than the angle of repose of the spent carbon-to-be-treated are provided in vertically multistage fashion on both the inner periphery of said outer cylinder and the outer periphery of said inner cylinder by vertically staggering the inclined annular plates of the outer cylinder relative to the inclined annular plates of the inner cylinder, and holes are provided through both the wall of said outer cylinder and the wall of said inner cylinder. The regeneration apparatus according to this proposition is constructed such that the spent carbon fed through the top of the annular regeneration chamber is subjected to high temperature heating, said heat being supplied through the outer cylinder wall while descending inside said chamber installed within the heating furnace, and also comes in contact with the regeneration gas, for instance, regeneration steam, diffused therein through the holes penetrating the inner cylinder wall, whereby the drying, calcination and reactivation progress, in order, downwards from the top of the chamber. At the same time, the moisture and adsorbed substances liberated from the spent carbon are in the form of gas diffused in the combustion zone within the heating furnace through the holes penetrating the outer cylinder wall together with the regeneration steam and are brought into contact with the high-temperature conbustion gas, whereby conbustible matters are incinerated. In this way, the apparatus is designed so as not to exhaust harmful and odorous substances to the outside of the system. Meanwhile, the present inventors have further studied the profile of heat consumption as viewed along the axial direction of the regeneration chamber at the time of effecting regeneration of the spent carbon by the use of the above proposed apparatus and discovered the fact that about half of the supplied quantity of heat is consumed in the drying process, hence an economical question arises. This drawback is considered as mainly ascribable to the fact that the spent carbon-to-be-treated usually contains approximately 50% of moisture and this wet active carbon is supplied as it is to a zone for a drying step which is identical with that for calcination and reactivation steps in requiring such a high temperature as in the range of from 800.degree. to 1000.degree. C. Besides, said apparatus is disadvantageous from the viewpoint of the cost of construction thereof, too. That is, in the regeneration process, said calcination and reactivation are particularly required to be performed in a high-temperature zone, so that the regeneration chamber must be built of expensive heat-resisting materials. Therefore, if the drying is to be performed in one and the same zone together with the calcination and reactivation, it will require the provision of a regeneration chamber with path elongated that much, entailing the enlargement of the heating furnace to accommodate said chamber.